Method for producing carbonized fabric

ABSTRACT

There is provided a carbonized fabric production method for producing a carbonized fabric by heating a fabric containing cellulose in a furnace, the method comprising: a fabric arrangement step; a first temperature-increasing step; a second temperature-increasing step; a maintenance step; a temperature-decreasing step; and a furnace-opening step.

TECHNICAL FIELD

The present invention relates to a method for producing a carbonizedfabric by heating a fabric containing cellulose in a furnace.

BACKGROUND ART

Charcoal obtained by carbonizing organic substances is used in variousfields. For example, it is used as a heating element due to its impartedconductivity and also used as an adsorbent due to its wide surface areaand its high porosity. Particularly, carbonized fabrics obtained bycarbonizing fabric are preferred as a planar heating element of a floorheating apparatus, a snow-melting apparatus, or the like.

The carbonized fabric can be generally produced by heating a fabricunder an inert atmosphere. However, there may be cases in whichconductivity is not imparted if the carbonization is insufficient.

CITATION LIST Patent Document

[Patent document 1] JP 2009429807 A

SUMMARY OF INVENTION Technical Problem

Therefore, an object of the present invention is to provide a method forproducing a carbonized fabric which may be used as a highly efficientheating element generating heat instantaneously after power supply.

SOLUTION TO PROBLEM

As means for solving the problem, the following invention and the likeare provided. Namely, there is provided a carbonized fabric productionmethod for producing a carbonized fabric by heating a fabric containingcellulose in a furnace, the method comprising: a fabric arrangement stepof arranging the fabric in the furnace; a first temperature-increasingstep of increasing a temperature of at least a fabric-arrangement regionin the furnace to a temperature that is closely below a carbonizingtemperature of the fabric, while at least the fabric-arrangement regionin the furnace being adjusted to be in an inert atmosphere; a secondtemperature-increasing step of, after the first temperature-increasingstep, of increasing the temperature of at least the fabric-arrangementregion in the furnace to a temperature in a range of from 1,200° C. to1,400° C., while at least the fabric arrangement region in the furnacebeing adjusted to be in a reducing atmosphere relative to at least theinert atmosphere in the first temperature-increasing step; a maintenancestep of maintaining, for a predetermined period of time, the temperaturein the furnace which has reached a temperature in a range of from 1,200°C. to 1,400° C. in the second temperature-increasing step; atemperature-decreasing step of gradually decreasing the temperature inthe furnace after a lapse of the predetermined period of time; and afurnace-opening step of opening the furnace after the temperature in thefurnace has become about 100° C. or less in the temperature-decreasingstep.

Furthermore, there is provided a carbonized fabric production method,wherein, in the above-described carbonized fabric production method, araw material of the fabric is cotton. Furthermore, there is provided acarbonized fabric production method, wherein, in the above-describedmaintenance step, the predetermined period of time is about from 1 to 2hours. Furthermore, there is provided a carbonized fabric productionmethod, wherein a period of time to be spent for the above-describedtemperature-decreasing step is 20 hours or more. Furthermore, there isprovided a carbonized fabric production method, wherein, in theabove-described furnace-opening step, opening and shutting the furnaceare performed intermittently so as to prevent a sudden decrease of thetemperature in the furnace.

ADVANTAGEOUS EFFECT OF INVENTION

According to the present invention, it is possible to provide a methodfor producing a carbonized fabric which may be used as a highlyefficient heating element generating heat instantaneously after powersupply.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart showing the flow of each step of a productionmethod according to the present embodiment.

FIG. 2 is an FE-SEM photograph of a carbonized fabric produced by theproduction method according to the present embodiment.

FIG. 3 is an FE-SEM photograph of the carbonized fabric produced by theproduction method according to the present embodiment.

FIG. 4 is an FE-SEM photograph of the carbonized fabric produced by theproduction method according to the present embodiment.

FIG. 5 is an FE-SEM photograph of the carbonized fabric produced by theproduction method according to the present embodiment.

FIG. 6 is an FE-SEM photograph of the carbonized fabric produced by theproduction method according to the present embodiment.

FIG. 7 is an FE-SEM photograph of the carbonized fabric produced by theproduction method according to the present embodiment.

FIG. 8 shows Raman spectroscopy results of the carbonized fabricproduced by the production method according to the present embodiment.

FIG. 9 is a conceptual diagram showing an application example ofcarbonized fabric produced by the production method according to thepresent embodiment.

FIG. 10 is a conceptual diagram showing another application example ofcarbonized fabric produced by the production method according to thepresent embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments according to the present invention aredescribed. The present invention is not to be limited to theseembodiments at all and may be implemented in various modes withoutdeparting from the gist of the present invention.

<Embodiment—Overview>

In the method for producing carbonized fabric according to the presentembodiment, the temperature in the furnace is increased to a temperatureclosely below a carbonizing temperature under an inert atmosphere, thenthe temperature in the furnace is further increased to a temperature ina range of from 1,200° C. to 1,400° C. while the atmosphere in thefurnace is adjusted to be in a reducing atmosphere, and the resultingcondition is maintained for a predetermined period of time. According tosuch a production method, it is possible to produce a carbonized fabricwhich may be used as a highly efficient heating element generating heatinstantaneously after power supply.

<Embodiment—Constitution>

FIG. 1 is a flow chart showing the flow of each step of the method forproducing carbonized fabric according to the present embodiment. Thepresent embodiment is a carbonized fabric producing method for producinga carbonized fabric by heating a fabric containing cellulose in afurnace. The method includes a “fabric arrangement step” (S0101), a“first temperature-increasing step” (S0102); a “secondtemperature-increasing step” (S0103); a “maintenance step” (S0104); a“temperature-decreasing step” (S0105); and a “furnace-opening step”(S0106), as shown in the figure.

The fabric of the present embodiment contains cellulose. The fabric is,for example, made by knitting or weaving vegetable cellulosic fibers,such as cotton, linen, silk, bamboo, paper mulberry or wood pulp.Alternatively, the fabric may be fabric made of regenerated fibers whichare manufactured by spinning natural fibers or polymers after dissolvingthem once. Examples of the fabric include, not only knit and wovenfabric but also non-woven fabric. The fabric is not necessarily limitedto be planar and may be string-shaped.

The “fabric arrangement step” (S0101) is a step of arranging the fabricin the furnace. The furnace may be any one capable of controlling thetemperature in the furnace, blocking outside air, and controlling theatmosphere in the furnace to be an inert atmosphere, a reducingatmosphere, or the like.

Examples of an embodiment of arranging the fabric in the furnace includearranging, in a stacking manner, the fabric which has been cut accordingto a size of an arrangement region, arranging the fabric which has beenfolded over and over without cutting, and arranging the fabric which isin a rolled state.

Although the region at which the fabric is to be arranged in the furnaceis not particularly limited, the fabric is preferably arranged in aregion where the temperature control and the furnace control asdescribed above are favorably performed. In other words, at the stage ofintroducing inert gas into the furnace, if there may be a region wherethe inert gas hardly reaches, it is not preferable to arrange the fabricin such a region.

In a case in which, in order to make the furnace atmosphere into areducing atmosphere, incomplete combustion is allowed to occur using aburner to generate carbon oxide, the fabric is preferably arranged sothat combustion flame is not in contact with the fabric directly or sothat the fabric is separated from the combustion flame with a refractorymetal or the like.

The “first temperature-increasing step” (S0102) is a step of increasingthe temperature of at least the fabric arrangement region in the furnaceto a temperature that is closely below a carbonizing temperature of thefabric, while at least the fabric arrangement region in the furnacebeing adjusted to be in an inert atmosphere. The carbonizing temperatureof the fabric, which varies according to materials, composition, etc. ofthe fabric, is generally about from 300° C. to 500° C. The fabricarrangement region is maintained under the inert atmosphere until thetemperature reaches a temperature at which the arranged fabric iscarbonized. Examples of the inert gas used for producing the inertatmosphere include nitrogen gas, helium gas, argon gas, and neon gas.Increasing the temperature under the inert atmosphere promotes thecarbonization without burning the fabric. The period of time to be spentfor the first temperature-increasing step is according to variousconditions such as material and quantity of the fabric, and volume ofthe furnace. The period of time to be spent for the firsttemperature-increasing step is, for example, about from 0.5 to 3 hours.In a case where the temperature is increased in an extremely shortperiod of time, the fibers constituting the fabric may be broken orsplit due to rapid volume change thereof.

The “second temperature-increasing step” (S0103) is a step of increasingthe temperature of at least the fabric arrangement region in the furnaceto a temperature in a range of from 1,200° C. to 1,400° C., while atleast the fabric arrangement region in the furnace being adjusted to bein an inert atmosphere, after the first temperature-increasing step.

“Being adjusted to be in a reducing atmosphere relative to the inertatmosphere in the first temperature-increasing step” means that anatmosphere in the furnace is adjusted so as to contain a larger amountof the reducing atmosphere than the inert atmosphere. Adjusting theatmosphere in the furnace into the relative reducing atmosphere promotesthe carbonization by a deoxygenation action to the fabric, and removesimpurities to produce a carbonized fabric having a high carbon purity.

Examples of the reducing gas used for producing the reducing atmosphereinclude carbon monoxide gas, hydrogen sulfide gas, sulfur dioxide gas,hydrogen gas, and formaldehyde gas. With respect to the introducing ofthe reducing gas into the furnace, the gas may be introduced directly.Alternatively, for example, a burner for combusting fuel gas such aspropane or butane may be provided in the furnace, and carbon monoxidegas may be produced by incomplete combustion. Alternatively, reducingmetal particles may be exposed in the furnace by sputtering, vapordeposition, or the like, so that the furnace atmosphere is made into thereducing atmosphere by reactions of these metal particles. Examples ofthe metal which may be used include lithium, cesium, rubidium,potassium, barium, strontium, calcium, sodium, magnesium, thorium,beryllium, aluminum, titanium, zirconium, manganese, tantalum, zinc,chromium, iron, cadmium, cobalt, nickel, tin, and zinc. Theabove-mentioned each process of producing the reducing atmosphere may beperformed simultaneously or may be performed step-by-step. Furthermore,the fuel gas of the burner, which is not limited to gas containing theabove-mentioned propane and methane with a purity of 100%, may be towngas in which an odorant such as thiol is added.

With regard to the carbonization of the fabric, crystallization ofcarbon proceeds better as the carbonizing temperature is higher.Although the crystallization occurs partially, the conductivity improvesthereby. On the other hand, embrittlement proceeds more intensely as thecarbonizing temperature is higher, so that a shape as the fabric may belost. Therefore, the temperature to reach in the secondtemperature-increasing step is determined as described above. Namely, ina case where the reached temperature is below 1,200° C., it may bedifficult to obtain the desired conductivity. Moreover, if the reachedtemperature is above 1,400° C., the embrittlement may proceedexcessively.

The period of time to be spent until the temperature in the furnacereaches the temperature to reach in the second temperature-increasingstep may appropriately be determined according to the material and thequantity of the fabric to be carbonized, the volume of the furnace, andthe like. For example, it is preferably about from 1 to 5 hours. If thetemperature is increased in an extremely short period of time, thefibers constituting the fabric may be broken or split due to rapidvolume change thereof. Conversely, even if increasing the temperature isperformed over an extremely long period of time, it is not mucheffective, so that it may be a waste of time and energy.

The “maintenance step” (S0104) is a step of maintaining the temperaturein the furnace which has reached a temperature in range of from 1,200°C. to 1,400° C. in the above-mentioned second temperature-increasingstep for a predetermined period of time. The carbonization is completedin the maintenance step. The period of time to be spent for themaintenance step is according to various conditions such as the materialand the quantity of the fabric, and volume of the furnace. For example,it is preferably about from 1 to 2 hours. If the period of time isshorter than 1 hour, the carbonization may be insufficient, so thatthere may be cases in which the desired conductivity cannot be obtained.Conversely, if the period of time is longer than 2 hours, theembrittlement may proceed.

The atmosphere in the furnace in the maintenance step may be the inertatmosphere or the reducing atmosphere. For example, the maintenance stepmay be performed under the reducing atmosphere continuously in so far asthe reducing gas introduced into the furnace in the secondtemperature-increasing step exists, or may be performed while theatmosphere in the furnace is made into the relative reducing atmospherein the same way as in the second temperature-increasing step. Asdescribed above, from the viewpoint of enhancing the carbon purity andremoving the impurities, it is preferable that the reducing atmosphereis maintained.

The “temperature-decreasing step” (S0105) is a step of graduallydecreasing the temperature in the furnace after a lapse of theabove-mentioned predetermined period of time. A sudden decrease in thetemperature in the furnace causes internal stress of the carbonizedfabric, so that heterogeneity of structure and properties may beintroduced to the carbonized fabric and the fibers constituting thefabric may be broken or split. This step is a step for preventing suchadverse effects. The temperature-decreasing step is performed under theinert atmosphere or the reducing atmosphere, similarly to theabove-mentioned maintenance step. Preferably, the temperature-decreasingstep is performed under the above-mentioned relative reducingatmosphere.

The period of time to be spent for the temperature-decreasing step isaccording to various conditions such as the material and the quantity ofthe fabric, and volume of the furnace. For example, it is preferably 20hours or more. By gradually decreasing the temperature in the furnaceover such a period of time, the above-mentioned adverse effects causedby the sudden decrease can be prevented.

The “furnace-opening step” (S0106) is a step of opening the furnaceafter the temperature in the furnace has become about 100° C. or less inthe temperature-decreasing step. In a case in which the furnace isopened in a state in which the temperature in the furnace is high, thecarbonized fabric may burn by contact with air. Therefore, to preventoccurrence of such a case, the furnace is opened after the temperaturein the furnace has become about 100° C. or less.

In the above-mentioned furnace-opening step, it is preferable thatopening and shutting of the furnace are performed intermittently tolower the rate of decrease in the temperature in furnace, rather openingthe furnace firstly and then maintaining the opened state. For example,when the furnace is first opened, the furnace is once shut immediatelyafter the first opening, and then the furnace is opened again. It ispreferable to intermittently repeat such opening and shutting of thefurnace. As described above, influence of the internal stress and thelike is preferably suppressed by performing the furnace-opening step soas to slowly lower the temperature in the furnace.

FIG. 2 is a photograph of a carbonized fabric produced by the carbonizedfabric production method according to the present embodiment, which wastaken at a magnification of 30 times by FE-SEM (Field Emission ScanningElectron Microscope). The fabric used for producing the carbonizedfabric is a fabric made by knitting natural cotton. FIG. 3 is aphotograph of the above-mentioned carbonized fabric, which was taken ata magnification of 100 times. FIG. 4 is a photograph of theabove-mentioned carbonized fabric, which was taken at a magnification of1000 times. FIGS. 5 to 7 are photographs of the above-mentionedcarbonized fabric, which were taken at a magnification of 10000 times.

FIG. 8 is Raman spectroscopy results of the above-mentioned carbonizedfabric. Using “NRS-3100 (JASCO Corporation)” as a spectrophotometer, themeasurement was performed five times (N=1 to 5) at difference places,under conditions of a laser wavelength 532 nm, a laser beam intensity of10 mW, an exposure time of 30 sec, and cumulative number of 2 times, tomeasure the “G band intensity (1,590 cm⁻¹)”, the “D band intensity(1,350 cm⁻¹)”, and the “Raman intensity ratio (D/G)”. According to themeasurement result, although the D band intensity is higher, the G bandintensity derived from graphite structure exists to a certain extent.Accordingly, it is thought that partial graphitization occurs.

The carbonized fabric produced by the production method according to thepresent embodiment may be applied as a heating element in various modes.FIG. 9 is a conceptual diagram showing a carbonized fabric which isapplied as a planar heating element. As shown in the figure, on theedges facing each other of the carbonized fabric (0901) according to thepresent embodiment, a positive long electrode and a negative longelectrode (0902, 0903) are attached respectively. By connecting a powersource (0904) to the positive electrode and the negative electrode andapplying voltage, the carbonized fabric generates heat instantaneously.Such an embodiment is suitable for realizing a floor heating apparatus,a snow-melting apparatus, or the like.

For example, on the two edge portions in a longitudinal direction of acarbonized fabric having a width of 150 mm and a length of 1,000 mm, apositive long electrode and a negative long electrode are providedrespectively. As a result of applying voltage adjusted to about 30 Vwith a transformer to the fabric, the current become about 3 A, and atemperature near a surface of the carbonized fabric reaches 80° C. in 2to 3 seconds after the voltage application. Furthermore, this heatgeneration occurs in the whole carbonized fabric without unevenness. Assuch, because of reaching the high temperature instantaneously after thepower supply, at an electric power of less than 100 W, it can beunderstood that the carbonized fabric is a highly efficient heatingelement.

FIG. 10 is a heating element made by encapsulating a fibrous carbonizedfabric (1001) in a quartz glass tube (1002) under vacuum. The carbonizedfabric having a string shape is provided with an electrode at each edgethereof, to which a power source (1003) is connected. This carbonizedfabric having a string shape generates heat as a result of applicationof voltage. Such an embodiment is suitable for realizing in a heatingapparatus, a heating cooking apparatus, a lighting apparatus, or thelike.

<Embodiment—Effect>

According to the carbonized fabric producing method of the presentembodiment, it is possible to produce a carbonized fabric which may beused as a highly efficient heating element generating heatinstantaneously after power supply.

REFERENCE SIGNS LIST

-   S0101 fabric arrangement step-   S0102 first temperature-increasing step-   S0103 second temperature-increasing-   S0104 maintenance step-   S0105 temperature-decreasing step-   S0106 furnace-opening step

1. A carbonized fabric production method for producing a carbonizedfabric by heating a fabric containing cellulose in a furnace, the methodcomprising: a fabric arrangement step of arranging the fabric in thefurnace; a first temperature-increasing step of increasing a temperatureof at least a fabric-arrangement region in the furnace to a temperaturethat is closely below a carbonizing temperature of the fabric, while atleast the fabric-arrangement region in the furnace being adjusted to bein an inert atmosphere; a second temperature-increasing step of, afterthe first temperature-increasing step, increasing the temperature of atleast the fabric arrangement region in the furnace to a temperature in arange of from 1,200° C. to 1,400° C., while at least the fabricarrangement region in the furnace being adjusted to be in a reducingatmosphere relative to at least the inert atmosphere in the firsttemperature-increasing step; a maintenance step of maintaining, for apredetermined period of time, the temperature in the furnace which hasreached a temperature in a range of from 1,200° C. to 1,400° C. in thesecond-temperature increasing step; a temperature-decreasing step ofgradually decreasing the temperature in the furnace, after a lapse ofthe predetermined time; and a furnace-opening step of opening thefurnace after the temperature in the furnace has become about 100° C. orless in the temperature decreasing step.
 2. The carbonized fabricproduction method according to claim 1, wherein a raw material of thefabric is cotton.
 3. The carbonized fabric production method accordingto claim 1, wherein the predetermined period of time is about from 1 to2 hours.
 4. The carbonized fabric production method according to claim1, wherein a period of time to be spent for the temperature-decreasingstep is 20 hours or more.
 5. The carbonized fabric production methodaccording to claim 1, wherein, in the furnace-opening step, opening andshutting the furnace are performed intermittently so as to prevent asudden decrease of the temperature in the furnace.